Planet Crackers?

Now this is entirely science fiction at the moment I was just speculating on the possibility of the planet cracker class starships that are found within the Dead Space universe. It seems to me though that if we ever become an interstellar civilization that planet crackers would be the best way to gather resources for humanity. Though it seems that it will not be technologically feasible until we are at least a type 2 civilization on the Kardashev Scale. The rather interesting thing about Planet Crackers is their gravity tethers which are powerful enough to remove significant portions of a planet's mass. I wonder how such a device could be created. Anyway I love the idea of planet crackers, and I hope that perhaps in the far future humanity will develop them.